This invention relates to a reaction arrangement for use in a brake booster to selectively communicate a first reaction force to balance a manual input force or a second reaction force to balance an electromagnetic input force to effect a brake application.
Vacuum brake boosters having a manual mode of operation and an electronic mode of operation are known in the prior art as evidenced by structure disclosed in U.S. Pat. Nos. 4,778,225; 5,096,267; 5,176,433 and 5,312,173 relating to the addition of traction control to a brake system and U.S. Pat. Nos. 5,226,173; 5,845,558; 5,772,290 and 6,065,388 relating to emergency braking features for a brake system. The structure in such brake systems functioned in an adequate manner for a purposed purpose at the time of such inventions however with the introduction of sway control features to a brake system such brake systems did not operate in a manner to provide for acceptable control of a brake system by an operator. For instance in some of the brake boosters having an emergency braking features, once an emergency brake application was initiated, the operator was prevented from intervening in the brake application unless the input force that initiated the emergency brake application was removed from a brake pedal. In U.S. Pat. Nos. 5,556,173 and 6,375,282 specific software and a switch activated by a brake light switch are disclosed to terminate an automatic braking. The shift in control of the operation of a brake booster is enhanced by the structure disclosed in U.S. patent application Ser. No. 10/645,206 filed Aug. 21, 2003 wherein an immediate transfer from an electronic actuation of a control valve to a manual actuation occurs so that the operation of the brake booster is under the control of an operator. While this brake booster functions in an adequate manner, the force required to initiate and sustain a brake application in response to a manual mode and an electronic mode is substantially the same and as a result, the size of an electromagnet member required to sustain an input force sufficient to oppose a reaction force corresponding to a desired brake application is relative large as compared to a size needed to activate a control valve.